The present invention relates to an optical signal add/drop apparatus, and more particularly, to an optical signal add/drop apparatus capable of adding and dropping simultaneously optical signals having various wavelength bands.
The optical signal add/drop apparatus is generally used for the optical signal transmission from a major optical transmission line of a bi-directional optical transmission system to a local network or metro core network, or for the optical signal transmission from a metro core network to a access network. That is, by using this optical signal add/drop apparatus, some optical signals having several specific wavelengths, among the optical signals that are transmitted through an optical transmission system from a region A (source) to a region B (destination), can be dropped from a region C and can be used in the network of the region C, and signals having the same wavelength as the dropped signals can be added and can be transmitted to B region.
Particularly, when optical signals having various wavelengths have been inputted into the optical signal add/drop apparatus used in a wavelength division multiplexing optical transmission system, the apparatus can simultaneously add a plurality of desired optical signals thereto and drop the desired optical signals therefrom.
FIG. 1 shows the constitution of a conventional optical signal add/drop apparatus that can simultaneously add and drop a plurality of optical signals.
As shown in FIG. 1, the conventional optical signal add/drop apparatus comprises a demultiplexer 10, a multiplexer 20 and a switch module 30.
The demultiplexer 10 divides multi-band optical signals xcex1 to xcexn inputted through optical fibers (input channels) into optical signals having respective wavelength bands, and transmits the divided signals through n optical fibers of output channel. The multiplexer 20 multiplexes optical signals having different wavelength bands inputted through the n optical fibers, respectively; and transmits the multiplexed optical signals to the destination through the other optical fibers (output channels). The demultiplexer 10 and the multiplexer 20 using thin film technology comprise a plurality of optical unit devices (not shown) for combining and separating the optical signals.
The switch module 30 comprises n set of 2xc3x972 switches for connecting respective optical signals received from the demultiplexer 10 with either of the optical fibers connected to the multiplexer 20 or the optical fibers connected to a local network 40.
In the optical signal add/drop apparatus constructed as such, multiple optical signals xcex1 to xcexn having n different wavelengths, inputted through the input channels, are separated in view of their wavelengths by the demultiplexer 10 and are transmitted through the respective optical fibers. According to connection state of 2xc3x972 switch, the optical signal may be dropped to the local network 40 or transmitted to the multiplexer 20. The optical signals may be inputted to the multiplexer 20, combined with the other signals having different wavelengths, and transmitted to the output channels.
However, since the conventional optical signal add/drop apparatus comprises a plurality of optical unit devices including the multiplexer, the demultiplexer and a group of the 2xc3x972 switches, there was a problem in that the size of the apparatus becomes larger. Further, since the expensive elements such as multiplexer, demultiplexer and the group of the 2xc3x972 switches should be used, there was another problem in that high costs of manufacture thereof are consumed.
Furthermore, since n optical unit devices should be provided, respectively, to the optical fiber grating typed or micro optics typed multiplexer and demultiplexer in case that there are n optical signals having different wavelengths, total 2n optical unit devices are used. Thus, the whole size of the apparatus becomes larger and the production costs thereof are more increased.
Accordingly, it is an object of the present invention to provide an optical signal add/drop apparatus that is small in size and is low in production cost.
Further, it is another object of the present invention to provide an optical signal add/drop apparatus wherein a plurality of wavelengths can be simultaneously dropped and added by multiplexing/demultiplexing portion, including a plurality of optical unit devices for simultaneously performing multiplexing and demultiplexing functions.
The optical signal add/drop apparatus for achieving the objects according to the present invention comprises: a first dual-core ferrule having first and second optical fibers disposed to be symmetrical to each other at identical distances from an optical axis for transmitting at least one optical signal; a second dual-core ferrule having third and fourth optical fibers disposed to be symmetrical to each other at identical distances from the optical axis for transmitting at least one optical signal; a wavelength division thin film filter for selectively transmitting only an optical signal having a specific wavelength; a first lens for collimating the optical signal inputted thereto from one of the optical fibers of the first dual-core ferrule into a parallel ray and outputting the parallel ray to the wavelength division thin film filter, and for focusing the optical signal reflected thereto from the wavelength division thin film filter and outputting the optical signal to the other optical fiber of the first dual-core ferrule; and a second lens for focusing the optical signal transmitted thereto from the wavelength division thin film filter and outputting the optical signal to one of the optical fibers of the second dual-core ferrule, and for collimating the optical signal inputted thereto from the other optical fiber of the second dual-core ferrule into a parallel ray, collimating the parallel ray to the wavelength division thin film filter, and outputting optical signal to the second fiber through first lens. Further, the first lens, the wavelength division thin film filter, and the second lens are arranged on the optical axis.
Multiplexing/demultiplexing portion including a plurality of optical unit devices and a switch module including a plurality of 2xc3x972 switches, connected correspondingly to the optical unit devices, respectively, for dropping the optical signal outputted from the optical unit device or adding the optical signal, identical to that dropped from the optical unit device, to the optical unit device.
The optical signal add/drop apparatus according to another aspect of the present invention comprises: an optical signal combining and separating portion including a plurality of optical unit devices which have a first dual-core ferrule having first and second optical fibers disposed to be symmetrical to each other at identical distances from an optical axis for transmitting optical signals, a second dual-core ferrule having third and fourth optical fibers disposed to be symmetrical to each other at identical distances from the optical axis for transmitting optical signals, a wavelength division thin film filter for selectively transmitting only an optical signal having a specific wavelength, a first lens for collimating the optical signal inputted thereto from one of the optical fibers of the first dual-core ferrule into a parallel ray and outputting the parallel ray to a first surface of the wavelength division thin film filter and for focusing the optical signal inputted thereto from the wavelength division thin film filter and outputting the optical signal to the other optical fiber of the first dual-core ferrule, and a second lens for focusing the optical signal inputted thereto from the wavelength division thin film filter and outputting the optical signal to one of the optical fibers of the second dual-core ferrule and for collimating the optical signal inputted thereto from the other optical fiber of the second dual-core ferrule into a parallel ray and outputting the parallel ray to a second surface of the wavelength division thin film filter; and a switch module including a plurality of switches connected correspondingly to the optical unit devices, respectively, for dropping the optical signal outputted from the optical devices or adding the optical signal, identical to that dropped from the optical devices, to the optical devices.
Herein, it is preferred that the switches be connected to the third and fourth optical fibers of the second ferrule, thereby being constructed in the form of the 2xc3x972 switches for dropping the optical signals outputted from the optical unit devices or adding the optical signals identical to the dropped optical signals.
Further, the first lens collimates the optical signal inputted through the first optical fiber into a parallel ray and outputs it to the wavelength division thin film filter. The first lens also focuses the optical signal, which is reflected by or passes through the wavelength division thin film filter, and outputs to the second optical fiber. The second lens collimates the optical signal inputted through the third optical fiber into a parallel ray and outputs it to the wavelength division thin film filter. Further, the second lens can focus the optical signal transmitted thereto from the wavelength division thin film filter and can output it to the fourth optical fiber.
Herein, the third optical fiber can be an add channel to which new optical signal is added from the local network, and the fourth optical fiber can be an drop channel through which the optical signal is dropped to the local network.